About fifty years ago, the American Piano Company attempted to encode expression of a keyboard instrument, typically a piano but also including a harpsicord, using a set of contacts spaced from one another in near proximity to the path of the piano hammer. Innumerable problems were encountered with this equipment, and they centered mostly around the adjustment of the contacts to control their spacing and positioning, permanent deformation of the felt on the hammer and other characteristics which are uniquely associated with the striking of the hammer in a piano. Another technique that has been discussed is the use of photocells to detect hammer passage. Inductive methods are not viewed with optimism because they require the addition of a coil or core metal to the hammer which would destroy the dynamics of the hammer system. This would make the hammer mechanism unwieldy or even worse, seriously alter its musical quality. The use of variable resistors is also viewed with some degree of apprehension because of the difficulty of linking hammer movement to a variable resistor and the resultant drag which would necessarily accompany its operation.
It has been discovered that it is possible to paint a thin layer of conductive material on portions of the hammer which do not actually strike the string. Hammers used in pianos and harpsicords are shaped in accordance with an industry standard. Hammers ordinarily include a striking portion and additionally have exposed surface which does not strike the string. This structure utilizes the remaining portions of the hammer head to construct a plate of conductive material thereon, albeit rather thin, so that it can be coupled by capacitive linkage to pads of conducting materials carried on a printed circuit board arranged approximately at right angles to the string. The capacitive pads are placed close to the path of the hammer. They are spaced sufficiently apart from the hammer path to avoid interfering with movement of the hammer as it strikes the string. This discovery, however, has had to deal with problems in working with capacitive coupling. The basic problem is that the size of the pads yields a very small capcitance typically in the range of about 0.5 to about 5.0 picarfarads. This, of course, presumes the use of relatively small pads which are painted, sprayed or otherwise placed on the hammer and having a width less than the thickness of the hammer head, an air dielectric, and pads constructed by suitable photoetching techniques on printed circuit boards.
The customary method of playing a stringed percussive instrument conveys the expression desired by the musician to the instrument itself dependent on two factors. The loudness of the note is determined by the force of striking the keys of the keyboard. Thus, a louder note requires crisper playing by the pianist. The duration of the note depends on how long the key is depressed.
In the playing of a piano which is the most typical keyboard instrument and also the most popular, it is customarily played with two hands. It is customary for the musician to divide the keyboard in halves so that the left hand plays the base notes and the right hand plays the treble notes. Other combinations of keyboard segregations can be used including octave or even singlenote groupings. On the other hand, the present invention encodes rapidly played notes with differing intensities. Thus, the musician may first strike a loud note (fortissimo) and thereafter strike a pianissimo note. The variety is unlimited; the apparatus can recognize levels of expression which, dependent on cost and complexity, range as high as 16, 32 or even 64 levels of expression.
The apparatus is particularly useful in forming a signal which is to be recorded with the musical notes actually played as taught in applicant's copending disclosure application Ser. No. 485,983 which was filed on July 5, 1974. In that disclosure, applicant has set forth a system for recording the notes actually played. This is therefor intended as an improvement or an addition to that structure; that apparatus discloses an apparatus and method whereby the notes actually played by the musician are recorded. This apparatus is preferably used with the tape recording system which is disclosed, and adds the expression so that, on playback, the melody is correctly played with the right expression (loudness and duration).
The referenced disclosure sets forth suitable recording apparatus. It also shows a playback system where the signals which are recorded by the present invention are converted into variable sized driving signals for solenoids to modulate their striking force and duration, thereby providing full expression on reproduction of the recorded music.